feat: close flyout when targeted session disappears

muxplex/frontend/app.js

@@ -1384,6 +1384,16 @@ function renderGrid(sessions) {
   var emptyState = $('empty-state');
   var filterBar = $('filter-bar');
 
+  // Close flyout if the targeted session no longer exists
+  if (_flyoutSessionKey) {
+    var flyoutStillExists = (sessions || []).some(function(s) {
+      return (s.sessionKey || s.name) === _flyoutSessionKey;
+    });
+    if (!flyoutStillExists) {
+      closeFlyoutMenu();
+    }
+  }
+
   var visible = getVisibleSessions(sessions);
 
   if (visible.length === 0) {

muxplex/tests/test_frontend_js.py

@@ -3953,3 +3953,14 @@ def test_render_grid_has_add_sessions_affordance() -> None:
     assert "add-sessions" in fn_body.lower() or "openAddSessionsPanel" in fn_body, (
         "renderGrid must render an 'Add Sessions' affordance for user views"
     )
+
+
+# ─── Task 12: Session death detection ────────────────────────────────────────
+
+
+def test_render_grid_closes_stale_flyout() -> None:
+    """renderGrid must close the flyout if the targeted session no longer exists."""
+    fn_body = _JS.split("function renderGrid")[1].split("\nfunction ")[0]
+    assert "_flyoutSessionKey" in fn_body or "closeFlyoutMenu" in fn_body, (
+        "renderGrid must check if the flyout's target session still exists and close if not"
+    )